The present invention generally relates to an apparatus and method for assisting in the diagnosis of myocardial ischemia of a human heart. The present invention is more particularly directed to an apparatus and method for providing data related to the activity of the human heart, wherein the apparatus is fully implantable beneath the skin of a patient and wherein the data provided may be utilized to advantage for determining the presence or absence of ischemia in the human heart.
Patients who suffer what is commonly called a heart attack most often experience an episode of myocardial infarction. Myocardial infarction is a necrosis of cardiac tissue brought on by a reduction in blood flow to the infarcted area caused by either an obstruction in an artery or a thrombus in the artery. Patients who have suffered from myocardial infarction are generally treated with drugs or surgery to open the artery or undergo coronary artery bypass graft surgery to bypass the artery section having the obstruction or thrombus.
Each of the above-mentioned therapeutic techniques is effective in reestablishing blood flow through the effected artery. However, for each therapy, there is a percentage of patients that experience restenosis (reclosure of the artery) after therapy. Restenosis is largely an unpredictable event and the time required for the reclosure to occur may range from a matter of hours to years.
To monitor patients who have suffered from myocardial infarction, physicians may rely upon periodic ECGs (electrocardiograms) which generally require as many as ten leads to be attached to the patient. In addition, after the ECG, physicians then generally require the patient to take a stress test wherein the patient is caused to run on a tread mill until the patient is essentially exhausted to stress the heart. During and after the tread mill exercise the twelve lead is used to determine if the heart continues to receive adequate blood supply while under the stress conditions. Obviously such monitoring is inconvenient to the patient. Physicians may also rely upon Holtor monitoring recordings which may last from 24 to 48 hours. These additional monitoring techniques are equally as inconvenient and in addition, are also annoying. Since all of these monitoring techniques can only be administered periodically at best as a practical matter, and because restenosis and thus future episodes of myocardial infarction are unpredictable events, all too often, a restenosis problem is not detected until the patient experiences pain or suffers an episode of myocardial infarction. Unfortunately, research has shown that pain is not a reliable indicator of ischemia.
From the foregoing, it can been seen that there is a need in the art for a new and improved monitor and method for monitoring patients who have suffered myocardial ischemia and thus may have a potential restenosis problem. The present invention provides such an apparatus and method because the apparatus is fully implantable beneath the skin of the patient and includes electrodes which are arranged to make electrical contact with the heart by, for example, being attached to or near the heart and to monitor heart activity in the form of an electrogram for each electrode. More particularly, the monitor of the present invention, monitors the electrogram from specific areas of the heart and more specifically, a predetermined electrogram parameter at each such area which has been shown to be reliable for indicating ischemia in the human heart. The apparatus is arranged to store the electrogram data for retrieval by the physician periodically and upon request by the physician through a command made by an external transmitter. As a result, the physician is provided with an early warning monitoring system of the state of the circulation in the patient's coronary arteries. As will be seen hereinafter, if the ischemia exceeds a predetermined limit, the apparatus provides the patient with a detectable alert signal informing the patient that the patient should consult his or her physician.